Question No. 01
A man can row three quarter of a km against
the stream in 11¼ min and return in 7½ min. The speed of the man in still water
is?
(A) 5 km/hr
(B) 7 km/hr
(C) 7.5
km/hr
(D) None of
these
Answer:
Option A
Explanation:
Upstream
speed = (3/4)/[(45/4) × 60] = (3 × 4 × 60)/(4 × 45) = 4 km/hr
Downstream
speed = (3/4)/[(15/2) × 60] = (3 × 2 × 60)/(4 × 15) = 6 km/hr
∴ Speed
in still water = (4 + 6)/2 = 5 km/hr.
Question No. 02
A boat covers 24 km upstream and 36 km
downstream in 6 hrs, while it covers 36 km upstream and 24 km downstream in 6½
hrs. The average speed of current is?
(A) 1.5
km/hr
(B) 1 km/hr
(C) 2 km/hr
(D) 2.5 km/hr
Answer:
Option C
Explanation:
Upstream
speed of boat = [(24 × 24) - (36 × 36)]/[(24 × 6) - (36 × 6.5)] = 8 km/hr
Downstream
speed of boat = [(24 × 24) - (36 × 36)]/[(24 × 6.5) - (36 × 6)] = 12 km/hr
∴ Speed
of current = (12 - 8)/2 = 2 km/hr.
Question No. 03
A man rows upstream 16 km and downstream 28
km, taking 5 hrs each time. The velocity of the current is?
(A) 2 km/hr
(B) 1.2
km/hr
(C) 2.4 km/hr
(D) 3.6 km/hr
Answer:
Option B
Explanation:
Upstream
speed = (16/5) km/hr
Downstream
speed = (28/5) km/hr
Velocity of
current = [(28/5) - (16/5)]/2 = 12/10 = 1.2 km/hr.
Question No. 04
If a man’s rate with the current is 12
km/hr and the rate of the current is 1.5 km/hr. Then the man’s rate against the
current in km/hr will be:
(A) 18 km/hr
(B) 22 km/hr
(C) 6 km/hr
(D) 9 km/hr
Answer:
Option D
Explanation:
Man’s rate
against current = Man’s rate against current - (2 × Rate of current)
= 12 - (2 × 1.5) = 9 km/hr.
Question No. 05
The current of a stream runs at 1 km/hr. A
motor boat goes 35 km upstream and back again to the starting point in 12 hrs.
The speed of the motor boat in still water is?
(A) 6 km/hr
(B) 9 km/hr
(C) 12 km/hr
(D) 14 km/hr
Answer:
Option A
Explanation:
35 = 12 (α²
- 1²)/2α
=> 6α² -
36α + α - 6 = 0
=> α =
6 or -1/6
We neglected
-ve sign, therefore
Speed of
boat in still water = 6 km/hr.
Question No. 06
A man can row 9⅓ km/hr in still water and
he finds that it takes him thrice as much time to row up than as to row down
the same distance in river. The speed of the current is?
(A) 6 km/hr
(B) 7½ km/hr
(C) 4⅔ km/hr
(D) None of
these
Answer:
Option C
Explanation:
Let, the
speed of current = α km/hr
Then, 28/3 +
α = 3 [(28/3) - α]
or, 4α = (2 × 28)/3
or, α = (14/3) km/hr = 4⅔ km/hr.
Question No. 07
A man can row at 5 km/hr in still water and
the velocity of the current is 1 km/hr. It takes him 1 hr to row to a place and
back. How far is the place?
(A) 2.4 km
(B) 2.3 km
(C) 2.8 km
(D) 2.5 km
Answer:
Option A
Explanation:
Distance =
[1 × (5² - 1²)]/(2 × 5) = 24/10 = 2.4 km/hr.Streams Aptitude: Next Tests